• Twelve children with acute abdominal pain, which was suspected of being acute appendicitis, were subsequently found to have lower lobe pneumonia. Diagnostic barium enema or operative exploration failed to demonstrate any appendiceal abnormality. The abdominal symptoms and the ileus subsided soon after the initiation of antibiotic therapy. Contrary to common belief, it was observed that left-sided pneumonia is capable of mimicking appendicitis almost as frequently as right-sided pneumonia. Since the likelihood of acute appendicitis accompanying pneumonia is small, operative intervention is rarely indicated and should be undertaken only after careful and intensive investigation.